<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- 1、求1 + 2！ + 3！ + 4！....+20!的值
	- 2！ = 2 * 1
    - 3！ = 3 * 2 * 1 -->
    <script>
        var jie=1;
        for(var i=1;i<=20;i++){
            jie*=i;
            // jie=jie*i;
        }
        document.write(jie);
    </script>
</body>
</html>